I don't like to interfere with weddings to get a picture, as soon as a photographer steps in all spontaneity is lost, turning a genuine moment into a contrived one.
Let a wedding flow, let people be people, let them relax and enjoy. Simply take the pictures while it happens without changing what's happening. Easier said than done and photographers often ask me how I get people to relax or not see me as a photographer, but rather as someone who belongs there and is just accepted as a guest, the honest answer is I don't know.
I guess it's all in the approach, I'm just really relaxed and genuinely happy to be a part of a wedding, I don't treat a wedding as a 'job', I'm a guest / friend / member of the family for the day, simply there to share the experience with everyone else.